1. Field of the Invention
The field of the present invention is couplings and closures for pipes and vessels, particularly as used in applications where high pressures, high temperatures and dirty and hazardous conditions obtain, and frequent or rapid opening is required.
2. Description of The Prior Art
Bolted flanges have been used to join sections of pipes and for blind flange closures on vessels and pipes for many decades. For many applications involving high pressures and/or temperature extremes, this approach, when used with suitable gaskets, has been satisfactory. To assure the safety of operations, most piping and vessel systems are designed to be in accordance with the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section VIII, Division I, and the American National Standards Institute (ANSI) Code for Pressure Piping (B31). Further, the ASME Code allows the use of flanges made to recognized Standards such as "Steel Pipe Flanges and Flanged Fittings", ANSI B16.5. Additional acceptable flange Standards are provided by the American Petroleum Institute (API) or the American Water Works Association (AWWA), for example.
The flanges that result from the application of these Codes and Standards employ a substantial number of bolts to secure the two flange faces together. The number and size of the bolts is determined from consideration of three factors - the pressure and temperature of the working fluid and the mechanical properties of the gasket. The selection of the configuration and material(s) of a gasket is dependent not only on the pressure and temperature of the material to be confined but the chemical nature of the working fluid as well. Gaskets that are suitable for high pressures and/or moderate to high temperatures require a high seating stress (i.e., the flange bolts must supply a large enough force to deform the gasket in order to obtain a good seal). Typical gasket materials for such services require a minimum seating stress of several thousand pounds per square inch (values range from a few hundred to greater than twenty-five thousand). As a result frequently more bolts are required to deform the gasket than are necessary to hold the pressure.
The assembly and disassembly of a large flanged joint connection with dozens of bolts is a very labor intensive and time consuming operation, but has been accepted because in most circumstances:
the vessel or piping closed by the joint contains no hazardous material when the joint is to be opened; and PA1 the work location is reasonably accessible; and PA1 the time needed to bolt and unbolt is acceptable; and PA1 the need to open the flanged joint is infrequent. PA1 the process equipment contains hazardous or toxic materials at the time the joint must be opened (i.e., gases, liquids and/or solids that present hazards to personnel such as pressure, temperature, toxicity, noise, radiation, etc.); and/or, PA1 the work location is not reasonably accessible (i.e., work area includes uncontrollable hazards nearby or is physically remote and dangerous); and/or, PA1 it is necessary to return the equipment to a functional status promptly (i.e., process or facility back on-line to maintain productivity); and/or, PA1 certain critical components are subject to relatively frequent failure, especially if an entire process or facility must be shutdown until replacement is effected.
For many operations where these four conditions do not prevail, however, and for flanges with diameters of about 24 inches or greater there has not been an attractive alternative to the bolted flanged joint. Industry has been obliged to use time consuming safety procedures to avoid exposing workers to hazardous fluids and to accept the large time losses involved in removing and replacing bolts.
Operators of industrial processes, as well as many research and development facilities, are concerned with two important characteristics of their operations -- productivity and safety. Not all industrial processes involve toxic materials or present dangerous working conditions. However, virtually all operations could benefit from a reduction in the time required for equipment maintenance or replacement and process reconfiguration. In a commercial setting a reduction in process down-time usually translates directly into increased plant throughput (i.e., increased marketable product or profit for the facility). In laboratory or experimental facilities, faster component replacement or equipment reconfiguration means greater flexibility in the conduct of experiments and a significant improvement in facility utilization.
A substitute for conventionally bolted flanges may be particularly desirable when any one or more of the following conditions exist:
Numerous "quick coupling" devices have been proposed during recent decades. In an attempt to replace the conventionally bolted flange, many designs employ a variation of the breech lock used in large artillery pieces -- usually a set of lugs mounted to one of the mating elements that provide mechanical interference with another set of lugs mounted to the other mating element, whereby the two elements must be rotated with respect to each other to effect locking.
In some designs a rotating ring is provided, thus eliminating the requirement that one of the mating components rotate relative to the other. Large autoclave closures are an example of this approach. FIG. 10 shows such an arrangement wherein a rotating ring includes pairs of opposing lugs which engage corresponding lugs on the mating elements. In order to provide an axial force to compress the seal or gasket between the elements, the lugs of one of the elements include wedges that ride against the lugs on the locking ring as it is rotated, causing the elements to be pressed together.
Both the breech lock and rotating ring approaches discussed above obtain lock-up of the connection through the action of sliding contact of metal surfaces, which is a fundamental weakness of these approaches, particularly in dirty and hazardous environments. High friction forces and the potential to gall the contact surfaces may also prevent the generation of the large axial force required to seat the gasket. Thus, the prior art devices are not particularly suited to withstand high pressure and high temperature and to be opened and closed many times without requiring repairs.